There is a great interest in the discovery of alternative sources of fuels and chemicals from resources other than petroleum. Development of non-petroleum-based liquid transportation fuels may provide economic and environmental benefits, while also increasing national security by decreasing reliance on non-domestic energy sources. Biomass, such as plants and animal fats, represent a major alternative source of hydrocarbons that can be converted into fuels. Liquid fuels derived from biomass are rapidly entering the market, driven by both need for increased national energy independence and rapid fluctuations in the cost of petroleum products. In 2007, the Energy Independence and Security Act was passed in the United States, which requires increasing quantities of bio-derived fuels to be produced over time. Similarly, the European Union directive 2003/30/EC promotes the use of biofuels or other renewable fuels. The directive has set a minimum percentage of biofuels to replace diesel or gasoline for transport purposes so, that by the end of 2010 there should be a 5.75% minimum proportion of biofuels in all gasoline and diesel fuels sold. To meet these mandates, it is essential to develop more efficient processes to convert bio-derived compounds into fuels that can fulfill these government mandates, as well as future global energy needs.
The carbohydrates found in plants and animals can be used to produce fuel range hydrocarbons. However, many carbohydrates (e.g., starch) are undesirable as feed stocks for creating biomass-derived fuels due to the costs associated with converting them to a useable form. The chemical structure of some carbohydrates makes them difficult to convert, and conversion processes may produce low yields of desirable products. Carbohydrates that are difficult to convert include compounds with low effective hydrogen to carbon ratios, including carbohydrates such as starches and sugars, and other oxygenates with low effective hydrogen including carboxylic acids and anhydrides, light glycols, glycerin and other polyols and short chain aldehydes. As such, development of an efficient and inexpensive process for converting one or more of these difficult-to-convert biomass feedstocks into a form suitable for use as a fuel additive could be a significant contribution to the art and to the economy.
Glycerol is a significant side-product of the trans-esterification reaction utilized to convert plant oils and animal fats into biofuels, and some work has been done examining ways to utilize glycerol. Karinen, et al. have reported methods for the etherification of glycerol and isobutene, while papers by Frustieri, et al. and Keplacova, et al., both include methods for catalytic etherification of glycerol by tert-butyl alcohol. U.S. Patent App. Pub. US2010/0094062 describes a process for the etherification of glycerol with an alkene or alkyne, followed by nitration of a remaining hydroxyl group. A portion of the process claimed in US2008/0300435 pertains to the dimerization/condensation of alcohols such as pentanol or isopropyl alcohol. However, to date, no methods have demonstrated an efficient process for the etherification of biologically-derived light glycol feedstock, such as ethylene glycol or propylene glycol, that results in a product suitable for subsequent use as a fuel additive.